Thermionic emitting device



July'13, 1948. z. J. ATLEE THERMINIC EMITTING DEVICE Filed July 3, 1944I Zea/JL/QZ/f@ uw 21% 904mg Patented July 13, 1948 THERMIONIC EMITTINGDEVICE.

Zed J. Atlee, Elmhurst, Ill., assigner to General Electric X-RayCorporation, Chicago, Ill., a corporation of New York Application July3, 1944, Serial No. 543,369*

This `invention'relates to electronics in general, and particularly toelectron-flow devices, such as electronic rectiers, X-ray tubes, radiotubes, and suchother devices as employ electron emitting elements. f

An important object of 'theinvention'is'the provision of a new andimproved electron emission element adapted to `beheated for electronemission at a relatively low temperature; a further object'being` to usecolumbium for electron emission. 1

Another'object of the invention is the provision, in an `electron ilow'device, of an electron emission element 'comprising columbium` supportedon a suitable structure such as tungsten, molybdenum, orOtherhighfmelting ypoint material.

Anotherobject of the invention is the provision of a columbium emitterindirectly heated, as bymeans of a suitable electrically energizedfilament, whereby 'electron emission is obtained at low operatingtemperaturesA well below the normal operating-temperature of =aconventional tungsten electron emitting filament, thereby renderingindeiinite life to the tube;` also, the heating 'of the anode is moreuniform and' the'emciency 'of the devicevis `greatly enhanced.

Another object of the invention is 'the' provision of an electronemitter'made of columbium,v either in the form of a strip, coil, tube orother wire;' a further object being toform the-emitter as asupportmember of material having a high meltingpoint and having a' coating `ofcolumbium vforming an emitting surface.V

A further object is to provide an electron flow device including ananode and a columbium electronemittingelement 'so' constructed andarranged that it will'shield a co-operating heater filamentlto thusprotect `the filamentr from the electrostatic force between it andtheanodewithout creating an undue space charge with respect toitheanodegto make possible a relatively large uniform emitting -srface ofthe cathode, to per mit the proper and ideal'design of the cathodefromthe standpoint of high voltage stresses, to make possible greater'electronic emission for a given amount ofheater or filament wattage, Aaswell `as to provide for greater eiliciency in general andmore ruggedconstruction.

A still further object is ythe provision'of an improved electronemitting element in the form of a cylindrical `member having a columbiumemitting surface. e v Still another object ofthe invention is to form anelectron emitting element lofcolumbium,and

`1 claim. (C1. 25o-27.5)

further that the thermionic emitting temperature of columbium issubstantially,1'700 to 190 Kelvin, being considerably lower thantungsten and tantalum, the two pure metallic thermionic emittersheretofore generally employed.

Numerous other objects'and advantages will be apparent throughout thefollowing specification. I

The :accompanying drawing illustrates a selected embodiment of theinvention,I andthe views therein are as follows: I

Fig. 1 is a sectional view taken longitudinally through an electronicrectifier embodying'the invention; f Y i Fig. 2 is a sectional view onFig. l;

Fig. 3 is a fragmentary sectional View showing a modified arrangement of4filament mounting; and f Fig. cathode structure ter is substantiallyelongated tering or gas absorbing eflect.

To illustrate the invention, the drawings show an electronv flow'deviceI embodying an anode 3 and 'a cathode 4 enclosed in a sealed envelope 2,suitable conductor ymeans being provided for connecting the `anode andcathode in electrical operating circuits externally of the envelope.While the invention is not limited to the shape of the anode, the sameis shown as a hollow cupshaped element enclosing the electron emittingportions of the cathode.

The electron emitting portion of the cathode comprises columbium whichfunctions to emit electrons ata temperature of 1700 yto 1900Kel vin.This is'substantially below thel temperature at which tungsten andtantalum emit electrons so that devices embodying my present inventionavoid the disadvantages inherent to devices embodying conventionalemitters.

' The columbium emitter element of my present invention may comprise anelement of pure metal, 0r the element may comprisea support of metal,suchv as tungsten or molybdenum, having a high melting point, thesupport being coated with columbium to form the electron' emittingsurface thereof.

The emitting element, however formed, may be heated for electronemission either by direct application of electric power to the elementor by mounting the element in position to be' the liner 2-2 of 4 is `adetail sectional view of a modified in which the columbium emittoprovide a getheated indirectly by suitable heating means.'

Where itis desired to heat the emitting element by direct electricalaction, the same maybe formed either as a coil, wire or strip of purecolumbium, or of other metal coated with columbum, and means may beprovided to connect the element with a suitable electrical power source.Where the element is heated by indirect action, it may be operativelyassociated with a suitable heater. To this end, the emitting element maycomprise a coil inductively associated with an induction coil or may beformed as a plate, strip or shell in heat exchange relation with respectto a heater, preferably an electrically energized coil or filament ofmetal such as tungsten.

The particular structure herein shown for the purpose of illustratingthe invention comprises an electronic device in the form of a rectifiertube I, although the several features of the invention are not limitedto rectifiers but may be utilized to advantage generally in electronflow devices, including X-ray tubes, radio tubes, and such other devicesWhere therrnionic emission is desired from a pure metallic source.

The rectifier tube I, as shown in the drawing, comprises a sealedenvelope 2 of suitable material, such as glass or metal, glass beingspecically shown in the drawing. The envelope 2 contains the anode 3 andthe co-operating cathode 4. The envelope 2 may be arranged in anyconvenient or preferred form, but is shown in the drawing as being atubular glass shell having re-entrant necks 5 at opposite `ends of theshell. The anode 3 and the cathode 4 are respectively supported on thesaid necks at the opposite ends of the envelope in any suitable fashion,although I prefer to employ supporting and sealing means of the sort'shown in my previous U. S. Patents Nos. 2,250,323 and 2,336,769,respectively issued July 22, 1941:and December 14,1943. In .thisconnection, the necks 5 denne `openings which are closed by seal members6 and I of generally cupshaped cong-uration. These seal members 5 and 1are preferably made of sheet metal, Each of said members '6 and 'I hasan annular rim which forms a glass-to-metal seal 8 with the inwardlyfacing end of the neck V5 on which the seal member is mounted, to thusseal the end of the envelope. y

The seal member l, at one end of the envelope, carries the anode 3.,which preferably comprises a. ytmp-'shaped element formed with a stem :9which projects outwardly of the end of the envelope through .an openingformed in the seal member l, -the stem 9 being sealed in said openingand carrying a bracket 9a, within the envelope, on 'the lcup-shapedanode element is mounted, as by rivets :or other fastening.

The :seal `member ll5, at the other end of the envelope, I'carries thecathode 4 which, as shown, preferably comprises an electron emissionlelement suitably mounted on support means carried by the seal .memberAIi.

According to the present invention, the electron emission velement`comprises fcolumbium and is preferably supported in position within andsurrounded by the cup-shaped yanode 3. The columbium emission elementmay be formed as a llament for direct connection in an electricalheating circuit or may be formed as a 'separate element and heated to aproper electron emitting temperature by 'a heater element I0 which -ispreferably made of tungsten.

The rcathode structure 4, as shown in Fig. 1, maybe ,mounted and sealedon the envelope by means -of Aa support and sealing structure of :thesort shown in my U. S. Patent No. 2,250,323, such structure comprising adisk-like `head Il., :preferably of metal, which head is mounted on astud I2 extending in an opening formed in the seal member 6, the studbeing sealed in said opening and having portions extending outwardly ofthe envelope. The hea-d II ycarries a tubular skirt I3 secured at oneend on the head and extending at the other end in position enclosing theglassto-metal seal 8. The skirt thus encloses a space I4 between theseal member E and the head II, which space is in open communication withthe interior of the envelope 2 through the annular space deiined betweenthe end of the skirt I3 and the glass-to-metal seal 8. Within thisspace, means may be provided for performing a gettering operation duringthe fabrication of the tube in order to insure the maintenance of -ahigh 4degree of vacuum within the envelope. This operation isaccomplished by means of a loop of gettering wire I9 in the space I4,said wire being connected at one end to the stud I2 and at the other endto a conductor 20 which lextends outwardly of the envelope through asuitable Vseal in the member t. By applying electric potential betweenthe wire 20 and an extension of the stud I2, outwardly of the envelope,the gettering wire may be'energized to perform its gettering functionwithin the envelope.

The opposite ends of the ilament I0 may he mounted on, electricallyconnected to, and supported by .conductor stems I5 and 2I which extendthrough openings I 6 formed in the head =I I. The ends of the stems maybe mounted yon and insulated from the head by fitting the openings IGwith grommets .I FI which receive the .stems I5 and 2| and which, inturn, are sealed in the openings as by welding or brazing. 'The lstemsare `supported in and electrically insulated from the grommets and thehead II by means of :globules of glass I'B; which support the ste-ms inthe grommet and seal the gramme-t opening :around the stems. Within thespace I 4, the ends of the stems I5 .and .21 are electrically connected,as tby clamps 22, with conductors .23 which extend through openings in.the sea-l member f6, said openings lbeing provided with grommets 24.,like the groirimets I 1, rin which the conductors 23 .are lsealed bymeans of glass globules simil-ar to the globules I8,` all as taught inmy aforesaid U. S. Paten-t'No. 2,250,323. lThe filament iI'Il thus iselectrically connected with the conductors :23 which extend outwardly-offthe envelope, such #connection being accomplished by way of fthestems =I 5 and 2:I which are electrically insulated from the head II.

The filament I0, Whichfis l,the heater for the cathode II, may be madeof columbium :and thus form an Ielectron emitter in :accordance with:the present invention, yor fthe lament may comprise tungsten coated-with columb-ium as .an emitter. However, the ilament vmay be usedmerely :as a heater element :en-closed .o1-'encased within a oylindricaltube r25 made of columbiumf-or Aof other metal coated with columbium.vIn ceither case, the tube `2li Wil-l 4have a columbium surface T26 lforemitting electrons. 'The :columbium cathode emitter .25 vis thusv:arranged to be indirectly heated by the heater which, in such case,may be made fof tungsten or other suitable material. While the drawingsdisclose .the use of a tubular or cylindrical columbium .emitter 25,itis of course understood that the emitter =`may be of any 'suitablesize and shape for the purpose intended; and the emitter may besupported on fthe head I'I in any suitable or convenient fashion, as'by-mounting it 'on support l'brackets 21 carried 7by one for other ofthefstems I 5 and 2i..

25cm-asv The use vof columbiumffor electronA emission in'-dire'ctlylieated bythe tungstenl lament IIJ produces'resultsgreatly'superiorto-any conventional electron' emission material; and theoperating temperature of a device embodying 'tlieinvention' is'considerably below rthat of'like devices employing other emissionmaterials. and still'v produces greater efficiency and effectiveness.IIlemperatures of'1700`t`o 1900 Kelvin obtain emission which is more4than adequate for various applications, and the temperature of thetungsten heaterfiilament is well below the normal operating temperatureof tungsten. Theuseof columbium as a cathode emitter does not producehigh space charges in the tube itself and still protects the lamenttoprevent the formation of any substantiali electrostatic force betweenthe. lament and the anode. The. heating of theI anode isL uniformwhereby localized. melting of the anodeis overcome. In addition', lowlamentcurrent eliminates the burning outoi' the filament. Moreover,thecathode emission per watt of filament consumption is very great. Irraddition, the thermionic emitting device, as herein disclosed andcomprising the columbiumtube or equivalent columbium structure, makespossible a large uniform emitting surface of the cathode, as well asmaking it possible for the proper design of a cathode from thestandpoint of high voltage stresses. Also, the use of columbium has thefurther advantage in that it can be formed more easily than tungsten,tantalum, or other emission materials. The thei'mionic emittingtemperature is approximately 600 Kelvin lower than tungsten, and therebyprolongs the life of the filament and the cathode emitter itself.Columbium makes possible more emission for a given heater or filamentwattage.

The tubular emitter 25 is preferably arranged concentrically about thetungsten filament I and may be supported in position by molybdenumribbons 21 welded or otherwise secured to the outside of the tube 25 andto the upstanding support stem 2l. The filament I0 is connected at itsupper end to the stem 2|, and at its lower end to the stem I5,preferably by wrappings of 5 mil (.005 inch) molybdenum wire, asindicatedat 28 in the drawing. The construction is such that thecolumbium tube is rigidly supported and is so arranged with respect tothe filament that there will be no obstruction to the emission oielectrons. It will be seen that the cathode emitter is electricallyconnected with one of the conductors 23, outwardly of the envelope,through the support stem and the molybdenum ribbons 21.

An electron flow device functions by the flow of electrons emitted fromthe cathode and traveling to and impinging upon the anode. When the flowdevice is constituted as a rectifier, the stream of electrons passingbetween the cathode and anode form a conduction path along whichelectrical current may iiow in one direction only between the anode andcathode. This uni-directional flow phenomena is utilized for the purposeof rectifying alternating or uctuating electrical energy in order toprovide uni-directional electrical power.

The columbium emitter 25, regardless of its shape or where its operativeposition may be, is capable of electron emission by indirect heatradiation or by electron bombardment through a diierence in potentialbetween the filament and the columbium. Also, the emission from thecolumbium may occur by the electronic bombardment `plus radiant heatAfrom the lament tothe columbium emitter.' f

' Fortungsten filament filament or heater' made oi columbium iil'amntmay be in the form of ,a helix, as shown, with respect to the tungsten,or the columbium filament may be a vtube or a strip orI it' may assumeany shape? proper toperform the functionintend'edy The-columbium emitterasgherein disclosed may be indirectly heated by co-operation-with aseparate heating filament, or may bei heated directly by making theheater or fiifament itself of columbium. i

In somev applications, as indicated in Fig. 3, it may'bed'esirable toground one or other vof the stems' I5 or2l o n the head l I instead ofmounting them both in insulating grommets. This may be accomplishedbypress-tting the stem to be groundediinv an opening or socket la, in thehead II-,` as' taught'inmy U-L S. Patent No.'2',250,323,"in whiel'i'caseone of the connection conductors 23 may be eliminated and connectionwith the grounded stem accomplished through the support stemI2,'outwardl'y of theenvelope;`rv` At leastone stemfhowev'er, mustbein'sulated from the head and end seal. Where one of the stems isgrounded, the emitter 25 may be connected either to the grounded or tothe insulated stem, but if connected to the insulated stem, the emitteralso must be insulated from the head I I.

As shown in Fig. 4, the columbium emitter 25 Ill'may be substituted a' vmay be provided with an integral elongated lower end 3l extendingconsiderably below the bottom end of the filament I0. The part of theemitter above the projection or elongation may attain a temperaturerange of between 1700 and 1900 Kelvin during operation. However, thetemperature range of the projection or elongation may vary from 1700"Kelvin at the upper end 32 of the elongation 3l to about 600 Kelvin atthe lower end 33 thereof. The elongation 3I acts continuously as agetter preventing the formation of gaseous matter within the envelope.The use of columbium, therefore, not only acts as a greatll7 improvedemission element, but when extended, as shown in Fig.4, the elongation3| acts as a gas absorber, eliminating gaseous material within theenvelope. In this embodiment, the lower end of the tube may be supportedon the head II and thus electrically connected thereto, in which caseelectrical connection with the emitter may be had outwardly of theenvelope through the stem I2 and its extension. To this end, it isdesirable to employ a modified cathode support structure of the sortshown in my U. S. Patent No. 2,336,769, in which the head I I issupported on and electrically connected with the seal member 6 by theskirt I3 instead of by the extension of the stem I2 inwardly of the sealmember. Elimination of the inwardly extending portion of the stem I2allows for supporting the stems I5 and 2l centrally on the head II.Alternately, the tube 25 may be supported on the head by suitableinsulating means, in which case electrical connection of the emitter maybe had outwardly of the envelope by connecting the tube 25 with one orother of the stems I5 or 20.

The tube 25 also may be formed with a closed top 34 whereby the filamentis entirely enclosed within the tube and thus completely shielded fromelectrostatic forces that otherwise might prevail between the anode andfilament when the device is in operation.

The invention provides an extremely efiicient thermionic emitting devicefor use in connection columbium, and suchwith rectifying tubes, X-raytubes, radio transmitting tubes, and other vacuum tubes where purethermionic emission is desired. The construction is such that the lamentls properly located and supported Without any obstructions, as is thecase where a spiral support is provided for the filament. Moreover, theuse of a columbium cathode emitter, indirectly heated by a tungstenfilament, or by making the lament of columbium for direct emission,permits lower operating temperatures well below the normal operatingtemperature of tungsten, thereby rendering indefinite life to the tube.The heating of the anode is uniform, and the efficiency of the device isgreatly enhanced. The use of the columbium as herein disclosed also actsas a getter in that gases within the envelope are absorbed oreliminated.

Changes may be made in the form, construction and arrangement of theparts without departing from the spirit of the invention, and the rightis hereby reserved to make all such changes as fairly fall within thescope of the following claim.

The invention is hereby claimed as follows:

An electron flow device comprising an enclosing envelope, a .cathodeemitter having a columbium surface arranged inside of said envelope, a.llamentheater arranged adjacent said surface and indirectly heating saidsurface, a conductor stem for the filament, and getter means ofcolumbium on the emitter extending below the end of the filament apredetermined distance and acting as a getter.

ZED J. ATLEE.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS

